This Collaboratory application focuses on the best understood reservoir for HIV-1, the latent reservoir in resting CD4+ T cells. Our goal is to find small molecule approaches for targeting this reservoir. However, HlV-1 may also persist in other reservoirs in patients on H/\ART. Therefore a comprehensive approach to HIV-1 eradication requires the identification of all stable reservoirs and the development of strategies to eliminate each one. To this end, our laboratory has been analyzing the trace levels of residual viremia (RV) that can be detected using specialized assays in patients on HAART who have "undetectable" viral loads by standard clinical assays. Because of the short half-life of free virus in the plasma, the presence of RV in patients on long term HAART indicates the ongoing production of virus in the presence of effective drugs. Thus, the analysis of RV provides a unique window into the state of virologic suppression and the reservoirs that stand in the way of eradication. Through sequence analysis of the trace levels of RV present in patients on HAART, our group and others have provided evidence that at least some fraction of the RV is derived from a source distinct from the latent reservoir in resting CD4+ T cells. The goals of the this project are to carry out exhaustive longitudinal sampling of the RV and the latent reservoir in unique patient populations and to compare the sequences from these two sources in order to verify the existence of additional reservoirs. Parallel studies will be carried out in SIV-infected macaques on HAART in a effort to find the source of the RV. Definitave demonstration of the existence of additional reservoirs contributing to RV will may require the development of alternative therapeutic approaches in addition to those targeting the latent reservoir in resting CD4+ T cells. Assessing the response of alternative reservoirs to strategies targeting the latent reservoir in initial clinical trials may provide critical information about the need for additional approaches to achieve eradication.